969114 - MediaCacheStream wastes about 10% memory in allocation slop

Status: RESOLVED FIXED

(Core :: Audio/Video, defect, P1)

Description

[Ben Kelly [:bkelly, not reviewing]]

DMD run on the poppit app on b2g v1.3 showed:

Unreported: 108 blocks in stack trace record 1 of 424
 3,981,312 bytes (3,579,552 requested / 401,760 slop)
 8.08% of the heap (8.08% cumulative);  20.07% of unreported (20.07% cumulative)
 Allocated at
   replace_malloc /srv/mozilla-b2g28_v1_3/memory/replace/dmd/DMD.cpp:1247 (0x4006e74e libdmd.so+0x374e)
   malloc /srv/mozilla-b2g28_v1_3/memory/build/replace_malloc.c:152 (0x400feeba libmozglue.so+0x23eba)
   moz_xmalloc /srv/mozilla-b2g28_v1_3/memory/mozalloc/mozalloc.cpp:53 (0x4182aefe libxul.so+0x132aefe)
   mozilla::MediaResource::Create(mozilla::MediaDecoder*, nsIChannel*) /srv/mozilla-b2g28_v1_3/content/media/MediaResource.>
   mozilla::dom::HTMLMediaElement::InitializeDecoderForChannel(nsIChannel*, nsIStreamListener**) /srv/mozilla-b2g28_v1_3/co>
   mozilla::dom::HTMLMediaElement::MediaLoadListener::OnStartRequest(nsIRequest*, nsISupports*) /srv/mozilla-b2g28_v1_3/obj>
   nsJARChannel::OnStartRequest(nsIRequest*, nsISupports*) /srv/mozilla-b2g28_v1_3/modules/libjar/nsJARChannel.cpp:966 (0x4>
   nsInputStreamPump::OnStateStart() /srv/mozilla-b2g28_v1_3/netwerk/base/src/nsInputStreamPump.cpp:517 (0x40895d2e libxul.>
   nsInputStreamPump::OnInputStreamReady(nsIAsyncInputStream*) /srv/mozilla-b2g28_v1_3/netwerk/base/src/nsInputStreamPump.c>

This shows that MediaCacheStream is wasting about 10% of the memory it actually requested in allocation slop.

This is due to the 32KB MediaCacheStream::mPartialBlockBuffer member array.  While it fits exactly in a power-of-2 allocation, the remaining member variables push it over into the next allocation size bigger.

This could be solved by allocating mPartialBlockBuffer separately on the heap.  This would be a minor win, but might be worth it given potential media use in games and other apps on b2g

Comment 1

[Ben Kelly [:bkelly, not reviewing]]

Attachment: Bug 969114: Avoid allocation slop in MediaCacheStream.

This moves the mPartialBlockBuffer to a separate heap allocation to avoid slop.

Comment 2

[Ben Kelly [:bkelly, not reviewing]]

Modest memory gains, but nom for 1.3t? since this is a low risk patch.

Comment 3

[Ben Kelly [:bkelly, not reviewing]]

Pushed to b2g-inbound with messed up and then corrected commit log again:

remote:   https://hg.mozilla.org/integration/b2g-inbound/rev/76e72417a9d7
remote:   https://hg.mozilla.org/integration/b2g-inbound/rev/b3150ee1da4d
remote:   https://hg.mozilla.org/integration/b2g-inbound/rev/b986786cf7dd

Sorry for the botched land again!

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/b986786cf7dd

Comment 5

[Joe Cheng [:jcheng] (please needinfo)]

triage: low risk, take this for tarako. 1.3T+

Comment 6

[[:fabrice] Fabrice Desré]

https://hg.mozilla.org/releases/mozilla-b2g28_v1_3t/rev/b5e941550a5b